In the field of heating devices, one type of heat source converts mechanical energy of motion into heat suitable for raising the temperature of a heat transfer fluid. This so-called "flameless" or "combustionless" heat source is inherently safer than those that derive their heat from burning an input material.
One method of employing this combustionless heat source operates according to pump-type principles. U.S. Pat. No. 3,333,771 to Graham is a representative patent showing this type of flameless heat source. The Graham patent discloses an arrangement wherein a heat transfer fluid or heating liquid is drawn through a rotor chamber and heated to a desired level by the rotational motion of a rotor mounted in the chamber. As built, this invention loses some of its mechanical energy to create discharge pressure at the head end or outlet of the rotor chamber.
Some of the disadvantages which characterize pump-type fluid heaters may be overcome by employing the friction generated between moving layers of fluid in lieu of the centrifugal motion of fluid particles to convert the energy of motion into heat. U.S. Pat. No. 4,143,639 to Frenette discloses a heat source wherein inner and outer drums are concentrically mounted to form a sealed, fluid-tight annular chamber between the exterior surface of the inner drum and the interior surface of the outer drum. A liquid captive in the annular chamber is heated via friction in response to relative rotation between the drums. Even though the Frenette invention manages to overcome the disadvantages of the prior art pump-type fluid heat sources, it fails to fully utilize the heat generated by the rotation of the drums. The heated fluid is retained inside the annular chamber and no efficient relationship is established to transfer the heat from the fluid to a position where it may be used.
U.S. Pat. No. 4,357,931, which issued to Wolpert et al on Nov. 9, 1982 disclosed a flameless heat source that used a vaned rotor rotatably supported within a cavity, and has inlet and outlet ports that temporarily block movement of a heat transfer fluid through the cavity. After the heat transfer fluid reaches a predetermined temperature, the rotation of the vaned rotor is stopped and the inlet and outlet ports are unblocked, thereby enabling the conduction of hot heat transfer fluid to a remote heat transfer surface. Although this invention overcomes the above-noted deficiencies of prior art flameless heat sources, it does have a time delay inherently built into it. The colder fluid is sent into the cavity and the inlet and outlet ports are blocked. Then the vaned rotor is moved to get the fluid heated to the appropriate temperature, and then the ports are unblocked to allow the heated fluid to flow to a transfer surface. The steps of blocking and unblocking the ports cause the time delay between when the demand for heat is sent and when the heat arrives.